This invention relates generally to hulls for watercraft which operate in a very high and ultra high speed range where hull resistance and propulsion requirements are of primary importance and in particular to a hull form embodying a specific planing, semi-displacement configuration which reduces resistance and power requirements at these high operating speeds. More specifically, the invention relates to a vessel having a hull form, that is, a shape, a cross-section, or a contour, that both displaces the water and that causes a force to be generated to raise the vessel out of the water.
Very high speed watercraft operate in two separate categories of hull resistance dynamics. Both categories involve potential theory concepts which relate energy input, from propulsion, to energy output from hydrodynamic pressures which create wave and pressure loads against the hull. Pressure loads create lateral wave profiles which act against the forward hull sections, which are lateral area profiles, to impede the forward motion of the hull. Pressure loads created by forward motion against the bottom surface of the hull sections act to lift the hull out of the water causing it to xe2x80x9cplanexe2x80x9d and thus decrease the impedance on forward motion of the hull created by the lateral wave profiles. A fully planing craft will ride completely on its bottom surface over the water surface so that the craft is lifted nearly completely out of the water and no longer behaves as an Archimedean (floating) body. In the modern design of very high speed vessels, the fully planing hull is not a realistic approach for the transport of cargo. Consequently, high speed craft involved in commercial enterprise typically operate in a speed range where wave making forces exert an important influence on hull design.
A truly viable commercial vessel operating at ultra-high speeds would be designed to take advantage of both minimal wave making and dynamic planing xe2x80x9cliftxe2x80x9d to decrease hull movement resistance and reduce the powering requirements of the vessel. Heretofore, wave making reduction in hull design has concentrated upon developing secondary wave systems which cancel out or reduce high bow waves or reducing wave making at specific areas of the hull rather than along the entire length of the hull. For example, increasing the stern closing wave height has not been addressed as a technique to decrease forward motion resistance. Bow appendages such as the xe2x80x9cbulbous bowxe2x80x9d projection have been successfully applied for full displacement, non-planing craft. These appendages are always extensions of the stem and keel, projecting ahead of the bow stem. Using bow projections as an appendage to planing craft has not proven effective since a planing craft by its nature xe2x80x9cliftsxe2x80x9d the hull out of the water so that the previously submerged bulbous bow projections during planing are partially out of the water and thus fail to function.
Wave drag reduction for hulls which operate at speeds where wave making and planing characteristics are combined has generally been frustrated by the complexity of the relationship between the two characteristics. Conventional approaches optimize one feature or the other, generally using horsepower to overcome the initial wave making hump at the fast speed range, where TQ=2.0, below optimal planing speeds. An approach which considers the entire immersed hull, the arrangement of immersed sectional areas over the length of the hull and the portion of the hull which can be optimized for a planing surface in conjunction with reduced wave drag has not been presented. Planing craft designed for ultra-high speed operations are typically designed to optimize the net area of the planing surface which develops the requisite xe2x80x9clift.xe2x80x9d As a consequence, the forward stations of a pure planing craft are full and are not designed to minimize wave making. The stern stations are as flat as possible since any wave closing augmentation is negligible as the hull is now riding nearly on the water surface due to dynamic planing xe2x80x9cliftxe2x80x9d.
Ultra-high speed craft engaged in cargo operations, where the size of the payloads is important, must operate in displacement and immersion levels where hull configuration and wave making continue to affect performance. This relates directly to the inherently immersed configuration of the hull form where wave drag characteristics are not removed or diminished by dynamic lift (or emergence) of the hull. The hull wave drag, given the design horsepower, must not be so great as to impede the ability of the hull to reach planing speed. At high speeds where TQ=2.0, conventional hulls exhibit an increase in wave making and create a resistance xe2x80x9chumpxe2x80x9d which stands in the way of a typically uniform increase in the power verses speed curve. This jump in resistance can only be overcome by applying more power to the vessel, very often more power than the vessel requires for its design speed once planing speed has been achieved and the wave making xe2x80x9chumpxe2x80x9d has been passed.
Thus, it is desirable to provide a semi-displacement hull which reduces wave making drag and it is to this end that the present invention is directed.
A hull form which operates in the speed ranges where both planing and wave making affect hull resistance is presented with a configuration which reduces wave drag and improves performance in very fast and ultra-fast speed ranges. The hull form is constructed so that there are variations in the distribution of immersed cross-sectional area that affect wave making resistance. The specific distribution of immersed cross-sectional area minimizes bow wave making and optimizes the closing wake. The bow wave impedes forward motion of a hull form. The stern closing wake pushes the hull forward and enhances the forward motion. The bow sections are designed so that they have a xe2x80x9chollowxe2x80x9d entrance configuration which decreases the effort to spread the water and in turn diminishes the wave making as the hull pushes through the water. The stem sections are designed to be of such a configuration that as the water spread by the bow now must close in around the stem of the hull, the wave height is increased so that the closing wake exerts a forward thrust on the hull. The stern wave caused by hull shape, is augmented or made higher, so that the bow sections reduce the wake height and the stern sections increase the wake height. The keel line at the bow has a slight upwards slope to allow for thinner bow sections and create hollow waterlines forward. The aft keel line has a long slope up and aft to allow for fuller and more nearly rectangular stem sections and create convex waterlines which form a slightly rounded side in the after body. Curving the afterbody section in towards the hull centerline increases the advantage of the closing thrust created by the stem wake. The sections aft of midships are all designed as low deadrise, hard chine sections where the dynamic lift surface for planing is optimized.
The semi-displacement hull in accordance with the invention significantly reduces the wave making drag of the hull at the high speed range (TQ=2.0) of vessel operation thereby allowing the vessel to reach ultra-high speeds where planing characteristics dominate hull behavior. The semi-displacement hull also includes an aft body that is developed for planing. The semi-displacement hull also may include derivative hull configurations, from a set of formulas, where hull coefficients may be varied. The invention also provides a multi-hulled high speed or ultra-high speed vessel using the semi-displacement hull.
The invention is a vessel intended for high and ultra-high speed operation and use in a semi-displacement mode where wave making and planing characteristics are present. The vessel has a semi-displacement hull with a semi-displacement forebody and an afterbody developed for planing. The hull form 1 is characterized by an immersed sectional area distribution and immersed sectional area providing a volume with concave surfaces in the forebody and convex surfaces in the afterbody. The forebody extends about 0.6 times the waterline length of the hull (0.6L) from the stem, and the afterbody extends thereafter to the stem. The stem is raked forward so that the waterlines from the stem to about 0.4 of the distance from the stem to the stem form concave contours, and the length of the bow keel slope is about one tenth the waterline length of the vessel. The bow keel has a slope less than 0.067 radians. The aft keel slopes up and aft at 0.69L from the stem and extends to the transom. The keel begins to slope up and aft 0.31L from the stem, and the elevation of the stem rise is less than 0.0266 radians.
The hull of the invention has specific parameters. For example, the average of the beam at the immersed chine and the beam at the load waterline, where B is the maximum beam at the waterline, H is the design draft, Ax is the maximum immersed cross sectional area, and B(n) is the beam at tenths of the waterline length along the waterline is given by the following:
B(2)=(0.388)(B) if [2HBxe2x88x92(1.395)Ax]/B is less than H;
B(3)=(0.664)(B);
B(4)=(0.838)(B);
B(5)=(0.936)(B);
and
B(6)=(0.976)(B).
Likewise, the immersed sectional area, An, at each one tenth of the distance from stem to stem, where n=1 through 11, and Ax is the maximum immersed cross sectional area, is given by
A1=(0.0334)Ax;
A2=(0.2707)Ax;
A3=(0.5735)Ax;
xe2x80x83A4=(0.7903)Ax;
A5=(0.922)Ax;
A6=(0.982)Ax;
A7=Ax;
A8=(0.982)Ax;
A9=(0.891)Ax;
A10=(0.701)Ax;
and
A11=(0.458)Ax.
The hull form is further characterized by the following parameters in the portion of the hull where the transition from displacement to planing occurs, that is, at approximately seven tenths of the distance from stem to stern, the hull is characterized by:
(a) an average beam B7=(0.993)(B),
(b) a height of the chine, C7,=2[H(B7)xe2x88x92Ax]/(B7), where Ax is the maximum immersed cross sectional area;
(c) a height of the keel, K11 at the stern above a base line is K11=2(H)xe2x88x92C7xe2x88x92[(1.7058)(Ax)]/(B);
(d) the slope of the keel, RK11,=K11/[(0.31)(L)];
(e) the height of the keel, Kn, at a station, n, aft of station 7, where n=8 through 11, is Kn=[(nxe2x88x921)(L/10)xe2x88x92(0.69)(L)](RK11); and
(f) the average of the beam at the chine and the beam at the load waterline, (Bn)=2(An)/(2Hxe2x88x92Knxe2x88x92C7).
Further hull parameters include the rise of the aft keel, measured from at least about 0.69L aft from the stem to the stern, has a aft keel slope that is less than 0.0266 radians from the horizontal line of the design baseline, a deadrise from 0.7L aft of the stem to the stern that is less then 18 degrees, and a rise of the bow keel less than 0.067 radians, extending from the stem to 0.1L aft of the stem to enable a concave waterline profiles in the forward sections of the hull.
In a further embodiment of the invention, the vessel has appendages to modify area distribution and wave making and planing characteristics. Typically, the appendages are sponsons.
In a further embodiment of the invention, the vessel has multiple hulls, as a catamaran.
In this way, the invention provides an ocean-going cargo vessel capable of high speeds where a combination of low wave drag and planing lift cause a reduction in powering requirements over other conventional hull forms. The invention also provides a vessel which has a suitably large block coefficient providing sufficient cargo capacity to create suitable revenues to justify the vessel""s use.
According to the invention, low hull resistance and reduced wave making are attained by a specific distribution of immersed cross-sectional areas, related to a specific design waterline draft, that creates a volume with concave surfaces in the forebody and convex surfaces in the afterbody and a specific alignment of the keel in reference to the baseline. The length of the forebody, or run of the entrance, is 0.6L from the forward point at the stem of the hull. The bottom surfaces of the hull are narrow with a high deadrise in the forebody and decrease as the entrance approaches the section of maximum cross-sectional area 0.6L from the stem and then continue on to the stern with a relatively low deadrise. The planing surfaces must be broad and relatively flat in order to optimize the lift provided by bottom pressures. This characteristic of broad, flat sections increases the wave making and is often at odds in very fast and ultra-fast hull designs. According to the invention, the wave making of the broad planing areas of the hull are used to add a forward component of thrust due to the closing wake generated by these broad planing areas.
A natural extension of hull area distribution is to use form modifiers which vary the area distribution of existing hulls to conform to the optimized distribution as proposed by this invention. For example, appendages to the side of the hull or sponson-like additions acting as form modifiers may be positioned where they are always immersed in a semi-displacement hull and operate effectively to reduce wave making.